1. Field of the Invention
The invention relates to a technique of reducing vibration of an impact tool, such as a hammer and a hammer drill, which rectilinearly drives a tool bit in a constant cycle.
2. Description of the Related Art
Japanese non-examined laid-open Patent Publication No. 2008-73836 discloses a vibration reducing mechanism of an impact tool that drives a tool driving mechanism by a ring-like member which is caused to swing in an axial direction of a rotary shaft by rotation of the rotary shaft and thus causes a tool bit to perform axial striking movement. This known vibration reducing mechanism is of a type that reduces vibration by a counter weight. The counter weight is connected to the ring-like member with a phase difference of about 180 degrees (opposite phase) in a circumferential direction from a connection between the ring-like member and a cylindrical piston (piston cylinder) of the tool driving mechanism. With such a construction, the counter weight is caused to move in the axial direction of the tool bit by swinging movement of the ring-like member, so that vibration caused in the axial direction of the tool bit during operation is reduced.
In the known vibration reducing mechanism using a counter weight, the structure of connecting the ring-like member and the counter weight has a radially extending columnar protrusion formed on an outer circumferential surface of the ring-like member and an engagement hole formed in the counter weight such that the connection is made by loosely inserting the protrusion into the engagement hole. Therefore, both the ring-like member and the counter weight must be specially designed for the connection.